This invention relates to a power limiter circuit that limits power supply voltage according to the value of the load resistance of transistor power amplifier.
The output of a transistor power amplifier with class B operation primarily varies with the load resistance value. Since the majority of speakers used today are 8 .OMEGA. and 4 .OMEGA., a large difference occurs in the power output of a transistor power amplifier depending on whether the loading is an 8 .OMEGA. or a 4 .OMEGA. speaker. If the power outputs resulting from 8 .OMEGA. speaker loading and 4 .OMEGA. speaker loading could be made the same, it would not only enhance amplifier thermal design and protect power transistors from excessive current flow but also an economical amplifier would result.
Further, although it is known to control the input of a transistor amplifier by sensing load current, circuitry for effecting this has a shortcoming in that waveform distortion or abnormal sounds occur due to the phase difference between voltage and current since the actual speaker is not purely resistive.